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Thursday, 10 April 2014

Where do viruses come from?

Principles of Molecular Virology, Chapter 3 (Virus Genomes), briefly discusses theories about the origin of viruses. But what does recent research tell us about where viruses may have originated?

Ask a first year student to draw a virus and, almost always, they draw a tailed bacteriophage (because that's what biology textbooks show). Ask them to describe virus infection of cells, and they invariably talk about virus particles injecting their genome into the cell "like a syringe". So they know about bacteriophage lambda (which is good), but what else is out there?

How does this diversity arise? It has been proposed that the last universal common ancestor (LUCA) of cellular life was infected by a number of viruses, and then specific virus groups adapted to infect the evolving cells that deviated to form the current three domains of cellular life. It has also been suggested that bacteria and archaea are infected by such different types of viruses due to the differences in their cell envelope composition. Archaeal viruses represent fossilized time and give us a glimpse back into the very origin of cells.